Photoresist is the light-sensitive film typically spun onto semiconductor wafers and exposed using high-intensity light through a photomask. The exposed photoresist (or the unexposed photoresist, depending on the polarity of the resist) is dissolved with developers, leaving a pattern of photoresist that allows etching to take place in some areas of the wafer, while preventing it in other areas of the wafer. Thus, photoresist is used in semiconductor fabrication primarily in the lithography or photolithography stages. Lithography itself generally is the process of pattern transfer.
Photoresist comes in different types, for different applications. For example, photoresist may be positive or negative photoresist, which generally indicates its amenability to being developed after exposure to light. Photoresist may be differently selective to different wavelengths of light as well. Resist may also expire, such that it has an expiration date after which it should not be used.
During the fabrication of semiconductor devices onto semiconductor wafers, it has generally been up to the technician or operator of the fabrication equipment to ensure that the proper bottle of photoresist is loaded for a given job. Mistakes made during photoresist switching, although quite rare (happening only three or four times a year, for instance), are quite catastrophic. If the wrong type of photoresist is loaded, or if an expired bottle of photoresist is used, a large number of semiconductor wafers may become ruined before the mistake is noticed. This can result in a large amount of financial loss to the fabrication foundry, as well as loss of goodwill from the customer.
For these and other reasons, therefore, there is a need for the present invention.